The present invention relates to soda-lime-based glass with a light color tone and a high light transmittance and to a method of manufacturing the same. Furthermore, the present invention relates to a glass sheet with a conductive film in which a transparent conductive film is formed on a surface of a glass sheet and to a method of manufacturing the same. In addition, the present invention relates to glass articles manufactured using the glass sheet with a conductive film, such as photoelectric conversion devices such as solar cells, multiple-glazing units, refrigerators, information displays, copiers, and the like.
Recently, lightly colored glass, particularly, hardly colored glass, so-called crystal clear glass tends to be preferred as building exterior glass. In addition, in the field of solar-electric power generation that receives attention again as a measure to reduce the carbon dioxide release amount and a countermeasure for fossil fuel exhaustion, there have been demands for a solar cell panel cover glass contributing to the improvement in power generation efficiency.
In order to meet such demands, conventionally, lightly colored high light transmittance glass has been used which is obtained by using high purity raw materials so that an iron content is reduced considerably as compared to that in conventional soda-lime-based glass.
A glass sheet with a conductive film in which a transparent conductive film is formed on a surface of a glass sheet is used in some applications. For instance, demands for such a glass sheet as low-emissivity glass (Low-E glass) have increased in a field of building window glass. In this field, in order to shield electromagnetic waves, a glass sheet with a conductive film may be used in some cases. The glass sheet with a conductive film also is used as a solar cell substrate. Furthermore, such a glass sheet also is provided as a base component of information displays such as liquid crystal displays (LCD), plasma display panels (PDP), or the like. The glass sheet with a conductive film also is used as a door plate of a display refrigerator for shops or a copier document plate.
Generally, in such applications, the glass sheet with a conductive film is required to have a high light transmittance. For example, in a solar cell, such a glass sheet is required to have a high transmittance in a wavelength region in which a photoelectric conversion device has high conversion efficiency. Similarly in various kinds of window glass, it is necessary to compensate for the decrease in visible light transmittance caused by the formation of a transparent conductive film.
A glass sheet with a conductive film can satisfy the aforementioned demands when using glass in which an iron content is reduced considerably as compared to that in conventional soda-lime-based glass.
The following description is directed to conventionally known high transmittance glass.
The glass disclosed in JP 4(1992)-228450 A contains, on a weight percent basis, less than 0.02% total iron oxide based on Fe2O3 as a coloring component and has a composition in which a ratio of FeO to the total iron oxide is set to be at least 0.4. In this glass, a visible light transmittance of at least 87% (measured with the illuminant C) can be obtained when the glass has a thickness of 5.66 mm. This glass sheet has been developed exclusively for furniture and provides a pure and bright azure color tone.
Aragonite as calcium carbonate mineral or hydrated aluminum is used as a raw material of the glass disclosed in the above-mentioned publication. Such a special material is used so that iron is prevented from being mixed as impurities. In addition, the above-mentioned glass also is characterized by being manufactured using a batch composition with a small SO3 content and being manufactured by a method including separate melting and refining stages as a melting operation.
A glass composition disclosed in JP 4(1992)-228451 A also contains a small amount of total iron oxide as described above and further contains trace amounts of Se and CoO. In this glass, a dominant wavelength of transmitted light is in a range of 570 to 590 nm, and this glass provides an appearance harmonizing with a wooden style. This glass also was developed exclusively for furniture.
Similarly in the glass disclosed in JP 4(1992)-228451 A, limestone or dolomite that contains a relatively large amount of iron oxide as an impurity cannot be used so that the amount of total iron oxide is suppressed to be less than 0.02% based on Fe2O3, on a weight percent basis, as in the glass disclosed in JP 4(1992)-228450 A. Therefore, a special material such as the calcium carbonate mineral described above is necessary, resulting in expensive glass.
In the glass disclosed in JP 4(1992)-228450 A, it is required to set the ratio of FeO to the total iron oxide to be at least 0.4 to obtain a desired pure and bright azure color. In order to obtain such a specific appearance, it is necessary to employ a special manufacturing method including separate melting and refining stages as a melting operation and to suppress the SO3 content, resulting in further expensive glass.
On the other hand, a method also has been proposed in which oxidizing agents such as cerium oxide is added, so that a content of FeO that is a principal component causing the decrease in transmittance in the above-mentioned wavelength region is decreased.
For instance, in the glass disclosed in JP 5(1993)-221683 A, 0.1 to 0.5 wt % CeO2 is contained as an oxidizing agent in conventional soda-lime-based glass containing 0.06 to 0.12 wt % impurity iron based on Fe2O3. In this glass, since a Fe2+/Fe3+ ratio is lowered considerably, a higher transmittance can be obtained in a wavelength region around 600 nm or longer. In this glass, the Fe2+/Fe3+ ratio is lowered to 3 to 10% from the ratio (38%) in the conventional soda-lime-based glass.
In this glass, since the Fe2+/Fe3+ ratio is lowered considerably, the absorption of light with wavelengths around 400 nm caused by Fe2O3 is increased. The increase in the Fe2O3 content causes the glass color tone to be yellowish. Such an appearance is not suitable, for example, for building window glass. In addition, the increase in the Fe2O3 content also lowers the light transmittance in a wavelength region around 500 nm or shorter. Such a transmission characteristic may be a hindrance when the glass is used as a substrate of an amorphous silicon solar cell having a high energy conversion efficiency in the wavelength region around 500 to 600 nm. Moreover, a relatively large amount of oxidizing agent is required for oxidizing a high concentration of iron. Therefore, the above-mentioned glass cannot always be manufactured at low cost.
None of the above-mentioned publications describes the formation of a transparent conductive film on a surface of a glass sheet.
With respect to the glass disclosed in JP 8(1996)-40742, consideration is given to the formation of a metal oxide coating film on a glass sheet. This glass was developed to be used for building windows and was developed for the purpose of shifting an absorptance in a near infrared region with the transmittance in the visible light region being maintained so that the absorption of solar radiation by glass windows is improved. According to the composition table specifically disclosed in the above-mentioned publication, this purpose is achieved through the reduction of a total amount of alkaline-earth metal oxide to be not more than about 10 wt % while an amount of Fe2O3 is comparable to that in conventional soda-lime-based glass. In this glass, the content of the alkaline-earth metal oxide is reduced and therefore, the wavelength region of light absorbed by FeO is shifted to the longer wavelength side.
However, the glass disclosed in JP 8(1996)-40742 is not suitable for use where a light color tone and a high transmittance are required, although the wavelength region of light absorbed by FeO is shifted to the longer wavelength side. In the above-mentioned glass, the amount of alkaline-earth metal oxide is reduced (namely, 9 wt % CaO and 0 wt % MgO in a composition example in the above-mentioned publication), and the inconvenience in melting caused by the reduction is compensated by an increase in the Na2O content. Therefore, liquidus temperature and manufacturing cost are high and thus the composition is not suitable for mass production.
It also has been known to increase the quantity of light passing thorough a glass sheet not by adjusting the composition of the glass sheet but by forming a reflection suppressing film (an antireflection film) on a surface of the glass sheet. An optical multilayer film with an optical interference effect is used as the reflection suppressing film in many cases. Generally, the reflection suppressing film is formed by a deposition method using vacuum equipment such as a sputtering method or a vacuum evaporation method.
As described above, the compositions of conventionally disclosed high transmittance glass are not suitable for industrial mass production at low cost.
In addition, the compositions of conventional high transmittance glass mainly were developed for specific applications requiring no transparent conductive film to be formed. Therefore, even when a transparent conductive film is formed on such high transmittance glass, it is not possible to mass-produce, at low cost, glass sheets with a conductive film having suitable characteristics for glass articles such as solar cells (particularly, amorphous silicon solar cells), multiple-glazing units, refrigerators, information displays, and copiers, which are the main applications of glass sheets with a conductive film. As to this point, the same is true even when the glass disclosed in JP 8(1996)-40742 A is used.
The present invention is intended to provide light-colored high-transmittance glass that can be mass-produced at low cost. The present invention also is intended to provide a method of manufacturing the light-colored high-transmittance glass at low cost. Furthermore, the present invention is intended to provide a glass sheet with a conductive film that has a high transmittance and can be mass-produced at low cost and to provide a method of manufacturing the same. In addition, the present invention is intended to provide glass articles in which such a glass sheet with a conductive film is used, specifically, solar cells, multiple-glazing units, refrigerators, information displays, and copiers.
First light-colored high-transmittance glass of the present invention formed as a glass sheet contains silica as a main component and is characterized by having a composition containing, as coloring components, on a weight percent basis:
0.02 to 0.06% (excluding 0.06%) total iron oxide (hereinafter referred to as xe2x80x9cT-Fe2O3xe2x80x9d) based on Fe2O3;
less than 0.024% FeO; and
0 to 0.5% cerium oxide,
having a ratio of FeO based on Fe2O3 to T-Fe2O3 (hereinafter referred to as xe2x80x9ca FeO ratioxe2x80x9d) of less than 40%, and having, when having a thickness of 3.2 mm:
a solar radiation transmittance of at least 87.5%; and
a visible light transmittance measured with the illuminant C of at least 90%.
Second light-colored high-transmittance glass of the present invention formed as a glass sheet contains silica as a main component and is characterized by having, when having a thickness of 3.2 mm:
a light transmittance of at least 91% at a wavelength of 500 nm; and
a light transmittance of not higher than 91% at a wavelength of 1100 nm.
These light-colored high-transmittance glasses have a high transmittance and can be mass-produced at low cost.
A method of manufacturing light-colored high-transmittance glass according to the present invention is characterized in that a raw material containing dolomite and limestone is used for the manufacture of the above-mentioned light-colored high-transmittance glass.
A glass sheet with a conductive film of the present invention is characterized by including a glass sheet made of the first or second light-colored high-transmittance glass and a transparent conductive film formed on a surface of the glass sheet.
A glass sheet with a conductive film that has a high transmittance and can be mass-produced at low cost can be provided through the formation of a transparent conductive film on a glass sheet containing the coloring components of the above-mentioned first light-colored high-transmittance glass.
In addition, a glass sheet with a conductive film that has a high transmittance and can be mass-produced at low cost can be provided through the formation of a transparent conductive film on a glass sheet having the optical characteristics of the second light-colored high-transmittance glass. In this glass sheet, the light transmittance is set to be not higher than 91% at a wavelength of 1100 nm, so that excessive increase in manufacturing cost is avoided. However, in the wavelength region around 500 nm in which amorphous silicon solar cells have high sensitivity and a man perceives brightness easily (visibility is high), the light transmittance is maintained to be at least 91%.
A method of manufacturing a glass sheet with a conductive film according to the present invention is characterized by including forming a transparent conductive film on a glass ribbon during a process of manufacturing the glass sheet by a float process using heat of the glass ribbon to manufacture the glass sheet with a conductive film.
In addition, according to the present invention, various glass articles in which the above-mentioned glass sheets with a transparent conductive film are used can be provided as described in detail later.
For instance, a photoelectric conversion device of the present invention is characterized by including the glass sheet with a transparent conductive film and a photoelectric conversion layer formed on a surface of the transparent conductive film of the glass sheet with a transparent conductive film. A thin film solar cell including a silicon layer as the photoelectric conversion layer is preferable as the photoelectric conversion device. Since the quantity of light passing through a substrate is related directly to photoelectric conversion efficiency, particularly, a glass sheet with a conductive film having a reflection suppressing film formed thereon as described later is suitable as a substrate for the photoelectric conversion device.
Furthermore, for instance, a multiple-glazing unit of the present invention includes at least two glass sheets positioned to oppose each other via one layer selected from an air layer, an inert gas layer, and a reduced pressure layer, and is characterized in that at least one of the glass sheets is the above-mentioned glass sheet with a conductive film. This multiple-glazing unit has an excellent visible light transmission characteristic and allows a natural view to be obtained.
In addition, for example, a refrigerator of the present invention is characterized in that the above-mentioned multiple-glazing unit is installed in a door and the transparent conductive film included in the multiple-glazing unit is used as a heating element (a defroster). Since this refrigerator mainly is used for display of sales products in shops and also has an excellent visible light transmittance, it allows goods to be displayed naturally while exhibiting a defogging function.
Furthermore, for instance, an information display of the present invention is characterized by including the above-mentioned glass sheet with a conductive film and displaying information through the glass sheet with a conductive film. Such information displays are not particularly limited but include LCD, PDP, and the like. Similarly in this information display, its high visible light transmittance enables clear and natural information displays, especially for color displays.
Moreover, for example, a copying machine of the present invention is characterized by including the above-mentioned glass sheet with a conductive film and optically readable information to be copied through the glass sheet with a conductive film. In this copier, the glass sheet is placed, for instance, in a document plate and the transparent conductive film exhibits an antistatic function and prevents paper jam or the like. In addition, its high visible light transmittance enables accurate copying, especially for color copying.
The glass sheet with a conductive film of the present invention can be utilized in various glass articles. The glass sheet with a conductive film of the present invention is different from the conventional high transmittance glass with a very low iron content developed for furniture and can be manufactured at a low cost while a required light transmission property is secured.